This invention relates generally to a new and improved pressure vessel and more particularly relates to an axially segmented pressure vessel providing, inter alia, economies of original cost, repair, assembly and disassembly.
Shown in FIG. 1 of the drawings is a typical prior art pressure vessel, indicated by general numerical designation 10, and associated with this pressure vessel are prior art pressure vessel problems and disadvantages overcome by the improved pressure vessel of the present invention. The pressure vessel 10 is illustrated schematically, in vertical cross-section, in context of a pressure vessel for hydrostatic extrusion apparatus including a piston 12 advancing or acting downwardly under the influence of pressure or force indicated by arrows 13 to pressurize and produce hydrostatic pressure in a body of pressure transmitting medium or hydrostatic fluid 14 to apply hydrostatic pressure indicated by arrow 15 to a billet 16 to hydrostatically extrude the billet through an extrusion die 17, in the manner known to those skilled in the hydrostatic extrusion art. The pressure vessel 10 includes a cylindrical liner 20 (typically made of a suitable high strength steel) surrounded radially outwardly by: cylindrical support member 22 (typically made of tungsten carbide), cylindrical support member 24 (typically made of a suitable high strength steel and typically segmented radially), a cylindrical taper ring 26 (typically made of a suitable high strength steel and whose taper is exaggerated in FIG. 1 for clarity of presentation), and a cylindrical support jacket 28 (typically made of a suitable high strength steel) press fitted over the taper ring 26 to apply inwardly directed force or pressure to pre-stress the liner 20 by producing circumferential compressive stress therein for opposing circumferential tensile stress produced in the liner by the pressurized pressure transmitting medium 14 which applies force or pressure to the liner 20 indicated by arrows 29 in FIG. 1. Thus, as understood by those skilled in the art, the circumferential compressive stress produced in the liner 20 by the press fit of the jacket 28 enhances the ability of the liner 20 to contain the pressurized medium 14.
Referring now to FIG. 2, the cylindrical liner 20 is illustrated schematically in perspective and an enlarged cube 30 of liner material is also illustrated schematically to provide a further understanding of the prior art problems and disadvantages associated with a prior art pressure vessel having a cylindrical liner, such as cylindrical liner 20, of unitary or non-segmented structure. As will be understood by reference to cube 30, internal pressure produced by the pressurized medium 14 (FIG. 1) is indicated by arrow 29 and produces circumferential tensile stress in the liner 20. As noted above, the press fit provided by the jacket 28 produces circumferential compressive stress in the liner indicated by arrow 31 in FIG. 2 for opposing the circumferential tensile stress. As further known by those skilled in the art, hoop stress, indicated by double headed arrow 32 in FIG. 2, will be the net circumferential stress produced in the cube 30, and hence in liner 20, by the opposed effect of the compressive and tensile stresses indicated by arrows 29 and 31. As is still further known to those skilled in the art, good pressure vessel design indicates that upon the pressurized fluid medium 14 (FIG. 1) being pressurized to its working level, such as for example for hydrostatic extrusion of the billet 16, the circumferential compressive stress indicated by arrow 31 and provided by the press fit of jacket 28 will exactly equal and thereby oppose or neutralize the circumferential tensile stress produced in the cube 30, and hence in liner 20, by the pressurized fluid medium 14. However, and as still further known to those skilled in the art, and as may be further understood by reference to FIG. 2, if axial compressive stress, indicated by opposed arrows 34 in FIG. 2 were to be applied to the cube 30, and hence to liner 20, such axial compressive stress will cooperate with the circumferential compressive stress indicated by arrow 31 to further oppose the circumferential tensile stress indicated by arrow 29 whereby the ability of the liner 20 to contain the pressurized medium 14 will be further enhanced.
The production of such axial compressive force in the liner 20, since it is of unitary or non-segmented structure, has an attendant problem which may be understood by reference to FIG. 3. The application of axially inwardly directed force or pressure to the opposed ends of the liner 20 does not produce uniform axial compressive stress throughout the entire length of the liner 20, indicated by length L1 in FIG. 3, but instead merely produces axial compressive stress at the opposed end portions of the length of the cylindrical liner which axial compressive stress decreases from each end to zero along the middle portion of the length L1 of the liner 20, and hence, the longer the length L1 of the liner 20, the less uniform axial compressive stress will be present along the entire length of the liner. However, as may be further understood by reference to FIG. 3, were the cylindrical liner 20 to be segmented axially along its length L1 into axially segmented lengths L2, L3 and L4, each such axially segmented length would experience the same generally axial compressive stress curve or profile as that of the longer length L1 but since the axially segmented length L2, L3 and L4 are shorter than L1, the axial stress in each such segmented axial length would not decrease to zero as shown and hence the net effect would be an average, and therefore substantially uniform, axial compressive stress along the axially segmented length L2, L3 and L4 as indicated by the averaging line A in FIG. 3. The improved pressure vessel of the present invention, as taught in detail below, provides such average, and therefore substantially uniform, axial compressive stress along the length of an axially segmented pressure vessel cylindrical liner.
Referring again to FIG. 1, and the typical prior art pressure vessel indicated by general numerical designation 10, it will be noted that the radially outward support members, for example the annular jacket 28, are also of unitary construction, are not segmented axially, and hence each such support member typically must be made from a relatively long forging. As further known to those skilled in the art, the longer the length of a forging the more expensive the forging and hence were such radially outward support members to be segmented axially they could be made from shorter forgings thereby reducing the cost of the pressure vessel. Also, it will be understood that the axial length of commercially available forgings is limited by the present technology and thus the shorter the length of the axial forgings required, the more competitive the sources and the less such forgings typically cost.
In addition, as will be understood, the longer the axial length of the radially outward support members, in particular the longer the axial length of the tapered annular support jacket 28, the greater the force required to press fit the jacket over the taper ring 26 and the other radially inward support members. The greater such force, the greater the cost of the equipment required to produce such force, and hence the greater the assembly cost of the pressure vessel and therefore the greater the cost of the pressure vessel; similarly, the greater the disassembly cost.
Still further, and referring again to FIG. 1, the longer the axial length of the cylindrical liner 20 the greater its cost and hence if the liner suffers damage at any point along its length, such as damage caused by galling due to foreign hard particles inside the liner, overpressurization of the liner, or axial misalignment of the piston 12 with the liner, the entire pressure vessel must be disassembled to repair or replace the liner and if the damage is sufficiently severe at any point the entire liner can require replacement.
As taught in detail below, the improved axially segmented pressure vessel of the present invention overcomes these additional prior art problems and disadvantages.